1. Field of the Invention
The present invention relates to a structure such as a door or wall of an environmental chamber and in particular a glazed door or wall.
The invention will be described more particularly for a door or wall of a refrigerated chamber in which cold or frozen products are displayed, but the invention is not limited to this type of chamber--any chamber with or without a hot humid environment also falls within the scope of the invention.
2. Discussion of the Background
When the products kept in a refrigerated chamber must remain visible, as is the case in many current commercial premises, the refrigerated chamber is equipped with glazed parts which transform it into a refrigerated "showcase," the common name for which is "refrigerated sales furniture." Many variants of these "showcases" exist. Some have the form of a cabinet, and then it is the door itself which is transparent, others constitute chests, and it is the horizontal lid which is glazed in order to allow the contents to be seen. While, yet others constitute counter-type showcases, and it is that part which separates the public from the merchandise which is glazed. Whatever the variant of these "showcases," it is also possible to produce glazed walls so that the entire content is visible from the outside.
The invention will be described more particularly for a door or wall of a refrigerated cabinet or chest.
In these types of display means, it is necessary for the merchandise to remain completely visible to customers so that it is possible to preselect the merchandise without opening the "showcase." Consequently, it is necessary to prevent the glazed parts of the "showcases" from becoming covered with condensation.
In order to prevent condensation, the method used generally consists in maintaining that face of the glazing assembly on the environment side at a temperature greater than the dew point of the atmosphere in question. This is achieved by increasing the insulation performance of the glazing assembly and, in addition, occasionally heating the face of the "warm" side. The simplest way of improving the thermal insulation performance of a single-pane glazing assembly is to replace it with a multi-pane glazing assembly. This technique is easy to implement in the case of cabinet-type showcases or in that of chest-type showcases, since the multi-pane glazing assemblies, consisting of two flat glass panels, mounted so as to be parallel to each other and separated by an air cavity or a gas-filled cavity, are easily fitted to the doors of cabinets or to the lids of chests. However, the use of such multi-pane glazing assemblies turns out not to be completely satisfactory from the thermal standpoint.
Several solutions have been envisaged for further improving the thermal insulation performance of these multi-pane glazing assemblies.
Thus, U.S. Pat. No. 4,382,177 relates to single-pane or double-pane glazing assemblies mounted in the doors of refrigerated cabinets or horizontal lids of chest-type freezers. The glazing assemblies are coated on their cold-side face with a film itself coated with a thin layer which reflects infrared radiation. By virtue of this thin layer, the insulation on the cold side is improved, the warm face is warmer and condensation occurs thereon at a higher water-vapor content of the ambient air. However, the improvement remains modest - the temperature rise is slight and the difference in moisture content of the atmospheres causing the condensation in both cases is low.
It is known to produce glazing assemblies consisting of 3 glass sheets, it being possible to replace one of the air cavities with a cavity filled with a gas such as krypton. These glazing assemblies have improved thermal insulation properties compared with the usual multi-pane glazing assemblies. However, these triple-pane glazing assemblies have a thickness such that there is a loss of transparency of approximately 25% compared with a monolithic glazing assembly. This reduction in visibility through the glazing assembly is further accentuated if at least one of the glass sheets is coated with a thin layer such as, for example, an infrared-reflective layer in order for the thermal losses through the glazing assembly to be significantly decreased. The loss of transparency is then such that it is necessary to increase the internal illumination of the chamber, thereby giving rise to an overall increase in the energy consumption of the environmental chamber.
It is also known to heat one face of a glazing assembly mounted in doors or walls of a refrigerated chamber above the temperature of the dew point of the "warm" ambient air. To do this, at least one of the glass sheets is coated on one of its faces with a thin conductive or semiconducting layer. There are numerous methods for depositing thin conductive or semiconducting layers on glass. In particular, several means are known which enable organic salts, which transform into conductive oxides, to be pyrolytically deposited on the hot glass. Among these, that of Patent EP-0, 125,153 allows continuous deposition of a thin layer based on fluorine-doped tin oxide on flat glass between the point where it leaves a "float" bath and where it enters the annealing lehr. This process makes it possible to obtain sheets of glass with a transparent and conductive layer of infinite dimensions for a low manufacturing cost. Such glazing assemblies coated in this way are generally heated continuously, especially if the temperature of the dew point of the "warm" ambient air is high. This continuous heating considerably increases the overall energy consumption of the refrigerated chamber.
Thus, U.S. Pat. No. 4,260,876 provides a heating control system applicable to refrigerated chambers. A system of sensors responds to the difference between the moisture content of the "warm," ambient atmosphere and the surface temperature of that part of the refrigerated chamber in question so as to control the heating energy consumption. However, such a system does not significantly decrease the overall energy consumption.
This is because, even if the heating is carried out intermittently, the heating times are generally longer than the non-heating times.
Moreover, whatever the approach envisaged by the manufacturer, it is usual to produce the glazed doors or walls from multi-pane glazing assemblies. Such glazing assemblies are very thick and heavy. Thus, because of their structure, it is necessary to fit them to a support frame which gives them good mechanical strength. In this way, these multi-pane glazing assemblies are bulky, which has repercussions on the structure and appearance of the chambers in which they are mounted.